Transformers typically use cores made of layers of magnetic steel in a stacked or core configuration. The magnetic steel used is typically silicon steel or, more recently, amorphous steel. Amorphous steel has several advantages over silicon steel insofar as core losses are concerned. However, after annealing operations, used to enhance the magnetic characteristics of the steel, amorphous steel becomes rather brittle and somewhat fragile. This can create problems in handling the core. It also can result in small flakes or particles of the amorphous material being released into the transformer oil within which the transformer is typically submerged. This creates a concern that such errant flakes of amorphous material could get in the windings to cause short-circuiting between windings, causing failure of the transformer.
Cores of wound transformer core material are somewhat unstable: they often have a tendency to unwind or telescope, and/or distort from their original shape, when handled. This is particularly true with amorphous steel which lacks bending stiffness within the plane of the material due to its thin structure. To prevent this from occurring, the ends of coiled core material have been sealed using various adhesives and resins. See, for example, U.S. Pat. Nos. 4,924,201 and 4,910,863.